Cholecystokinin (CCK) and gastrin (G) are regulatory peptides which are found in gastrointestinal tissue and in the central nervous system, Mutt, Gastrointestinal Hormones. Glass, Ed. Raven Press, N.Y., p. 169 (1980). The CCK peptides reportedly co-exist with dopamine in certain mid-brain neurons, and thus may play a role in the functioning of dopaminergic systems in the brain, as well as serving as neurotransmitters, Prange et al., Ann. Repts. Med. Chem. 17: 31 (1982). Gastrointestinal CCK and gastrin may act on parietal and chief cells of the fundic glands of the mammalian gastric mucosa to stimulate acid and pepsinogen secretion, Chew and Hersey, Am. J. Physiol. 242: G504 (1982). Cholecystokinins are also believed to be physiological satiety hormones and, thus, may play a role in appetite regulation, Smith, Eating and Its Disorders, Stunkard and Steller, Eds., Raven Press, N.Y., p. 67 (1984). Additional effects of CCKs include the stimulation of colonic motility, gall bladder concentration, pancreatic enzyme secretion and the inhibition of gastric emptying.
Intestinal CCK exists in 39- and 33-amino acid forms with the C-terminal 33-amino acid residues being identical. Biological activity is restricted to the C-terminal heptapeptide of the native peptide and a C-terminal octapeptide has the same efficacy as CCK-33 but is approximately ten-times more potent, Jensen et al., Proc. Natl. Acad. Sci. USA 77: 2079 (1980).
Gastrin also occurs naturally in several different forms; 34-amino acids, 17-amino acids and 13-amino acids with the tyrosine being either sulfated or unsulfated. The 17- and 13-amino acid forms can be viewed as C-terminal fragments of the 34-amino acid form. The different forms exhibit varying potency for stimulating gastric acid secretion. Gastrin-17 is 5 times more potent than Gastrin-34 and 2.5 times more potent than Gastrin-13, Walsh and Grossman, New Engl. J. Med. 292: 1324,1377 (1975). Gastrin and CCK share a common C-terminal pentapeptide amide sequence, Gly-Trp-Met-Asp-Phe-NH.sub.2.
Gastrin and CCK antagonists are useful for treating diseases mediated by gastrin and CCK. CCK antagonists are successful in preventing or treating CCK-related disorders of the gastrointestinal, central nervous and appetite regulatory systems of animals, especially of humans. Antagonists of CCK are also useful in potentiating and prolonging opiate-mediated analgesia and thus have utility in the treatment of pain, Faris et al., Science 226: 1215 (1984). Gastrin antagonists are useful in the treatment and prevention of gastrin-related disorders of the gastrointestinal system in humans and animals, such as ulcers, Zollinger-Ellison syndrome, antral G cell hyperplasia and other conditions, in which reduced gastrin activity is of therapeutic value. CCK and gastrin also have trophic effects on certain tumors, Ohyama, Hokkaido J. Med. Sci., 60, 206 (1985), and antagonists of CCK and gastrin may be useful in treating these tumors.
Antibiotics of the Virginiamycin family have been used as food additives to improve the growth of poultry, swine and cattle. Although growth promotion by antibiotics is not thoroughly understood, there is little doubt that the effect is due in part to an inhibition of the intestinal flora, Coccito, Micro. Rev. 43: 145 (1979). Virginiamycin M.sub.1 and related antibiotics are generally specific for gram-positive bacteria and prevent cell multiplication. The virginiamycin antibiotics are most effective when in their complex form, that is when they are composed of both M and S components, Coccito, Micro. Rev. 43: 145 (1979). The wide use of these antibiotics as growth promoters relates their low toxicity, lack of accumulation in animal tissues, no production of resistant mutants and a rapid degradation in animal feces.